You're right about the seed currently being a bigger source of revenue and profit than RoundUp, because it's currently protected by patents whereas the herbicide patent expired in 2000, and now Monsanto is being undersold on generic glyphosate (without its special additives) by Chinese chemical producers who have been incentivized and subsidized by their government.

However, RoundUp seed patents begin expiring with soybeans first in 2014, and it looks like canola will follow a year or three later.

RoundUp (the herbicide) apparently accounts for 10% of Monsanto's revenue, but the corresponding seed will soon account for zero.